# Système International Prefixes: Part 2

In my previous post about the Système International prefix system, I described how they originated in the French Republican metric system of 1795, which introduced a set of prefixes to designate multiples and fractions of its base units.

For instance, the metre was subdivided using prefixes into decimetres, centimetres and millimetres, designating a tenth, hundredth and thousandth part of a metre, respectively. Multiples of the metre were the decametre, hectometre, kilometre and myriametre, indicating tenfold, hundredfold, thousandfold and ten-thousandfold multiples, respectively.

In Part 1, I dealt with the fractional prefixes, all of which are Latin, and all of which are still with us to a greater or lesser extent. This time, I’m going to talk about the prefixes used for multiples, which are all Greek.

Deca- comes from Greek deka, “ten”. It gives us decade, a period of ten years; decad, a group of ten things; and decurion, a Roman soldier, subordinate to a centurion, who was in command of only ten men. A decapod has ten feet—shrimps and lobsters belong to the order Decapoda. And Giovanni Boccaccio‘s story collection The Decameron describes events that take place over ten days—from deka combined with Greek hemera, “day”.

The Decalogue refers to the Ten Commandments of the Old Testament. In the nineteenth century Arthur Hugh Clough offered a satirical reworking, The Latest Decalogue:

Thou shalt have one God only; who
Would be at the expense of two?

No graven images may be
Worshipped, except the currency.

Many doctors nowadays quote his version of the Sixth Commandment, “Thou shalt not kill; but need’st not strive / Officiously to keep alive,” as if it were a medical maxim, apparently unaware that Clough was writing satire.

Hecto- is from Greek hekaton, “hundred”. It appears in the name of the hectograph, a Victorian precursor of the photocopier. Hekaton gave us hecatomb, in Greek and Roman times a huge public sacrifice of a hundred oxen, and nowadays a mass killing. A hecatontad is a group of a hundred things. A hecatomped (yes, that’s the correct spelling) is not a hundred-footed thing (that job being already taken by the word centipede), but something a hundred feet square—it’s an architectural term, applied to Greek temples; as is hecatonstylon, a building having a hundred pillars.

Hecto- hasn’t had much luck as a prefix, and has tended to fall into disuse. It mainly lingers on in the hectare, a non-SI unit of area, equal to 10,000 square metres. (The are was the unit of area measurement in the original French Republican metric system, equal to one hundred square metres.)

Kilo- is an odd one. It comes from the Greek chilias, “thousand”—but why the French, who are no great users of the letter “k”, should have adopted that particular spelling is a bit of a mystery. (To me, at least.)

A chiliad is a group of a thousand things. A chiliander is something containing a thousand men—an overblown description of a warship. And chiliasm is a Greek synonym for a Latin term I mentioned in Part 1, millenarianism—the belief that Christ will return to Earth to rule for a thousand years. A chiliast is one who subscribes to chiliasm—a millenarian, in other words.

And, astonishingly, the Greeks found a use for the word chiliomb—an analogue of the hecatomb, except involving the sacrifice of a thousand animals. You certainly wouldn’t want to be in charge of clearing up after one of those.

Myria- comes from Greek myrias, “ten thousand”. A myriander was an even more unlikely warship that a chiliander—containing ten thousand men. A myriad was originally a group of ten thousand things, but the difficulty of actually counting that many of anything has led to a drift in meaning towards “uncountably many”. So a myriapod has uncountably many legs—it’s a catch-all term for the group of arthropods that includes the centipedes and millipedes.

Myria- has fared very badly as a multiplicative prefix, and has gone down into extinction. H.G. Wells made an effort to give myriad a new quantitative meaning in his 1910 novel, The Sleeper Awakes. In that story a man sleeps for two centuries, and awakens to discover that the decimal system of numbers has been abandoned in favour of a duodecimal system (based on the number 12):

“Yes. Six dozen, Sire. Of course things, even these little things, have altered. You lived in the days of the decimal system, the Arab system—tens, and little hundreds and thousands. We have eleven numerals now. We have single figures for both ten and eleven, two figures for a dozen, and a dozen dozen makes a gross, a great hundred, you know, a dozen gross a dozand, and a dozand dozand a myriad. Very simple?”

H.G. Wells The Sleeper Awakes (1910)

By my reckoning, Wells’s myriad was equal to 2,985,984. We’ll need to wait for the rise of the duodecimal system before that catches on.

That about wraps it up for the French Republican metric prefixes. They were already inadequate to describe the world when they were introduced—it was known, for instance, that the Earth was four thousand myriametres in circumference, which was already understood to be a very small distance in comparison to the scale of the solar system. And microscopists were routinely examining objects on a scale of a thousandth of a millimetre.

More prefixes were needed, to expand the scale both upwards and downwards. That’s what I’m going to write about in Part 3. In the meantime, if you want to know more about the French invention of the metric system, I can recommend Robert Tavernor’s Smoot’s Ear: The Measure of Humanity.

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